Non-linear ECAP Feedback for Spinal Cord Stimulation
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Solution Overview
Problem
Spinal cord stimulation systems face challenges in maintaining consistent pain relief due to lead migration, which causes changes in stimulation energy and impedance, leading to over-stimulation or under-stimulation, and requires time-consuming training periods assuming a linear relationship between ECAP signal amplitude and lead-spinal cord distance.
Innovation Solution
A system with a processor that senses evoked compound action potentials (ECAPs) to adjust spinal cord stimulation therapy based on feedback differences, maintaining a constant current flux density at the target tissue site by accounting for changes in lead position and tissue properties, using a non-linear relation to adjust stimulation parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead position changes due to patient movement or migration, then stimulation energy delivery changes, but this causes over-stimulation or under-stimulation leading to loss of therapy effectiveness
Solution Approach 1:
The system continuously monitors ECAP signals and uses this feedback to automatically adjust stimulation parameters. The ECAP amplitude serves as a real-time indicator of lead-spinal cord distance, enabling the system to compensate for lead migration and maintain consistent therapeutic effect despite position changes
Solution Approach 2:
The system dynamically adjusts stimulation parameters (amplitude, pulse width) based on detected ECAP signal changes. When ECAP amplitude decreases indicating lead migration, the system increases stimulation parameters to maintain constant current flux density at the target tissue
2Device complexity
If linear relationship between ECAP signal amplitude and lead-spinal cord distance is assumed, then calibration is simplified, but this assumption is incorrect and reduces measurement precision
Solution Approach 1:
The system performs preliminary non-linear calibration to establish the actual relationship between ECAP amplitude and lead-spinal cord distance for each patient. This pre-characterization creates a lookup table or mathematical model that enables accurate distance estimation without requiring complex real-time calculations during operation
Solution Approach 2:
The system replaces the incorrect linear mathematical model with an empirically-determined non-linear model based on actual physiological responses. This substitution of the relationship model improves measurement accuracy while maintaining computational efficiency through pre-computed correction factors
3Ease of operation
If stimulation parameters are not adjusted for lead position changes, then device operation is simple, but this results in over-stimulation with high charge injection causing tissue damage risk
Solution Approach 1:
The system automatically monitors its own performance through ECAP detection and self-adjusts stimulation parameters without requiring manual intervention. This self-regulating capability maintains safety by preventing over-stimulation while keeping the device simple to operate, as the adjustment occurs autonomously based on physiological feedback
4Reliability
If stimulation parameters are increased to compensate for lead migration, then paresthesia coverage is maintained, but this increases energy consumption and may cause over-stimulation
Solution Approach 1:
The system applies stimulation parameters that are precisely sufficient to maintain constant current flux density at the target tissue, avoiding both under-stimulation and excessive energy delivery. By using ECAP feedback to determine the exact compensation needed, the system delivers only the necessary amount of energy rather than excessive stimulation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the safety and efficacy of spinal cord stimulation by compensating for changes in stimulation thresholds and maintaining consistent paresthesia coverage, reducing variability as the patient moves or the lead migrates, thereby enhancing pain management.
Implementation Method 1
sensing circuitry configured to sense an evoked compound action potential (ECAP) response that propagates along the neural pathway
Data Source
AI summary
A system of non-linear feedback control for spinal cord stimulation is provided. The system comprises a lead adapted to be implanted within an epidural space of a dorsal column of a patients spine, and a pulse generator (PG) electrically coupled to the lead. The PG is configured to deliver spinal cord stimulation (SCS) therapy. The system also comprises a sensing circuitry configured to sense an evoked compound action potential (ECAP) response that propagates along the neural pathway. The system also comprises a processor programmed to operation, in response to instructions stored on a non-transient computer-readable medium, to obtain a baseline ECAP response when the lead and spinal cord tissue properties are in baseline states; analyze ECAP responses relative to the baseline ECAP response to obtain an ECAP feedback difference indicative of a change in at least one of the baseline state of the lead and the baseline state of the spinal cord tissue properties. The processor is also programmed to adjust an SCS therapy based on the ECAP feedback.